1. Field of the Invention
This invention relates to a gas sensor and a method for detecting a gas such as CO gas contained in a small amount in air flowing into a space between electrodes which is ionized by a radiation source.
2. Description of Prior Art
Heretofore, there has been known an inoization type smoke sensor which detects presence of aerosol (small particles suspended in air) entering a space between a pair of electrodes inonized by a radiation source. For example, U.S. Pat. No. 3,521,263 issued July 21, 1970 to Thomas Lampart and Andreas Scheidweiler proposes that a field strength of the ionized space be 5 V/cm or less to easily detect a combustion gas (aerosol) produced by a fire.
On the other hand, development of a gas sensor which is capable of detecting a deoxidizing gas such as CO, H.sub.2, etc. arises recently, and there has been proposed a gas sensor which detects a gas such as CO contained in a small amount in air with a detecting mechanism similar to that of the conventional ionization type smoke sensor.
However, the mass of a gas molecule such as CO is as small as 1/10,000 of that of the aerosol (smoke particles), object of detection in the conventional smoke sensor. The detection of small gas molecule such as CO cannot be attained by mere selection of the field strength 5 V/cm as suggested in the U.S. Patent.